Configurable Power Module For AC And DC Applications

ABSTRACT

In an embodiment, a power module may include: a plurality of first stages, each having an H-bridge to receive an incoming AC voltage at a first frequency and rectify the incoming AC voltage to a DC voltage; a plurality of DC buses, each to receive the DC voltage from one of the plurality of first stages; a plurality of second stages, each coupled to one of the plurality of DC buses to receive the DC voltage and output a second AC voltage at a second frequency; and a hardware configuration system having fixed components and optional components to provide different configurations for the power module.

BACKGROUND

Various power conversion systems are used to convert and conditionpower, to more efficiently provide power from a given power source.Regardless of the type, these systems are typically formed of multiplepower converters, often implemented as modules. While these modules canbe desirably customized for particular applications, there are notstandard modules that can be used in different applications.

SUMMARY OF INVENTION

In one aspect, a power module for use in a power conversion system isprovided. The power module may include: a plurality of first stages,each of the plurality of first stages comprising an H-bridge to receivean incoming AC voltage at a first frequency and rectify the incoming ACvoltage to a DC voltage; a plurality of DC buses, each of the pluralityof DC buses coupled to receive the DC voltage from one of the pluralityof first stages; a plurality of second stages, each of the plurality ofsecond stages coupled to one of the plurality of DC buses to receive theDC voltage and output a second AC voltage at a second frequency; and ahardware configuration system having fixed components, where the powermodule is a configurable module.

When the configurable module is adapted in a first power conversionsystem, the hardware configuration system includes the fixed componentsand optional components; and when the configurable module is adapted ina second power conversion system, the hardware configuration systemincludes the fixed components and not the optional components.

In an example, the fixed components comprise a plurality of jumperconnector points, and when the configurable module is adapted in thesecond power conversion system the plurality of jumper connector pointsare unconnected, and when the configurable module is adapted in thefirst power conversion system the optional components comprising one ormore jumpers are coupled to at least some of the plurality of jumperconnector points.

In an example, when the configurable module is adapted in the firstpower conversion system, the plurality of first stages are coupled inseries via the one or more jumpers coupled to the at least some of theplurality of jumper connection points.

In an example, the one or more jumpers comprise a first set of jumpersto serialize the plurality of first stages.

In an example, the one or more jumpers further comprise a second set ofthe jumpers coupled to the plurality of first stages to enable a bypassoperation to occur.

In an example, the power module further comprises a controller coupledto the plurality of first stages and the plurality of second stages,where the controller, in a first mode, is to configure the power modulefor unidirectional power flow, and, in a second mode, is to configurethe power module for bidirectional power flow.

In an example, the power module further comprises a circuit board onwhich the plurality of first stages, the plurality of DC buses, theplurality of second stages, the hardware configuration system, and thecontroller are adapted.

In an example, the circuit board comprises a central portion on whichthe controller is adapted, a first peripheral portion on which theplurality of first stages are adapted, and a second peripheral portionon which the plurality of second stages are adapted.

In an example, the power module further comprises: a first plurality ofindependent heat sinks, each of the first plurality of independent heatsinks associated with one of a first plurality of switches of theplurality of first stages; and a second plurality of independent heatsinks, each of the second plurality of independent heat sinks associatedwith one of a second plurality of switches of the plurality of secondstages.

In an example, the circuit board is foldable such that the firstperipheral portion and the second peripheral portion fold inwardly tooppose each other, and the circuit board, when folded, is an enclosurefor the power module.

In an example, when the configurable module is adapted in the firstpower conversion system, the configurable module is configured as anAC-AC converter; and when the configurable module is adapted in thesecond power conversion system, the configurable module is configured asan DC-AC converter.

In another aspect, a power module comprises: a circuit board having aplurality of layers comprising conductive traces; a plurality of lowfrequency (LF) bridge circuits adapted on a first portion of the circuitboard, each of the plurality of LF bridge circuits to receive anincoming voltage and output a DC voltage; a plurality of DC busesadapted on the circuit board, each of the plurality of DC buses coupledto receive the DC voltage from one of the plurality of LF bridgecircuits; a plurality of high frequency (HF) bridge circuits adapted ona second portion of the circuit board, each of the plurality of HFbridge circuits coupled to one of the plurality of DC buses to receivethe DC voltage and output a second voltage; and a controller adapted ona third portion of the circuit board, the third portion located betweenthe first portion and the second portion, and wherein the circuit boardis foldable such that when folded, the circuit board forms an enclosurefor the power module.

In an example, the power module comprises a configurable power module,and: when the configurable power module is included in a first powerconversion system, each of the plurality of LF bridge circuits is toreceive the incoming voltage comprising the DC voltage; and when theconfigurable power module is included in a second power conversionsystem, each of the plurality of LF bridge circuits is to receive theincoming voltage comprising an AC voltage and rectify the AC voltage tothe DC voltage.

In an example, the controller is to configure the power module forprovision of a charging DC voltage to an EV charging system, wherein thepower module further comprises a plurality of jumpers coupled to aplurality of jumper connection points adapted on the circuit board, tocouple a midpoint of the plurality of LF bridge circuits to enable theplurality of LF bridge circuits to provide the charging DC voltage.

In an example, the power module further comprises: a first plurality ofindependent heat sinks, each of the first plurality of independent heatsinks associated with one of a first plurality of switches of theplurality of LF bridge circuits; and a second plurality of independentheat sinks, each of the second plurality of independent heat sinksassociated with one of a second plurality of switches of the pluralityof HF bridge circuits.

In an example, the power module further comprises a plurality of jumperconnector points adapted on the circuit board, where when the powermodule is included in a first power conversion system the plurality ofjumper connector points are unconnected, and when the power module isincluded in a second power conversion system at least some of theplurality of jumper connector points are coupled to one or more firstjumpers, wherein the plurality of LF bridge circuits are in a parallelconfiguration in the first power conversion system and the plurality ofLF bridge circuits are in a series configuration in the second powerconversion system.

In an example, when the power module is included in the second powerconversion system, one or more second jumpers couple to at least othersof the plurality of jumper connector points to enable bypass of at leastone of the plurality of LF bridge circuits.

In another aspect, an EV charging system comprises: a plurality of firstconverters to receive grid power at a distribution grid voltage andconvert the distribution grid voltage to at least one second voltage,each of the plurality of first converters comprising a configurablemodule to receive an AC or DC distribution grid voltage; at least onehigh frequency transformer coupled to the plurality of first convertersto receive the at least one second voltage and to electrically isolate aplurality of second converters coupled to an output of the at least onehigh frequency transformer; and the plurality of second converterscoupled to the output of the at least one high frequency transformer,where at least some of the plurality of second converters are to receivethe at least one second voltage and convert the at least one secondvoltage to a third DC voltage and provide the third DC voltage as acharging voltage or a charging current to one or more EV chargingdispensers, each of the plurality of second converters comprising theconfigurable module to receive the output of the at least one highfrequency transformer and output the third DC voltage or an AC voltage.

In an example, the configurable module of the at least some of theplurality of second converters comprises a plurality of jumpers coupledto at least some of a plurality of jumper connector points of theconfigurable module to configure the configurable module as a buck/boostconverter to output the third DC voltage to the one or more EV chargingdispensers.

In an example, the configurable module of the at least one of theplurality of second converters to output the AC voltage does not includethe plurality of jumpers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an environment in which an EVcharging system accordance with an embodiment may be used.

FIG. 1B is a block diagram illustrating another environment in which anEV charging system accordance with an embodiment may be used.

FIG. 2 is a block diagram of an EV charging system in accordance with aparticular embodiment.

FIG. 3 is a block diagram of an EV charging system in accordance withanother embodiment.

FIG. 4A is a schematic diagram of a power module in accordance with anembodiment.

FIG. 4B is a block diagram of a power module in accordance with anembodiment.

FIG. 5A is a schematic diagram of a power module in accordance withanother embodiment.

FIG. 5B is a block diagram of a power module in accordance with anotherembodiment.

FIG. 6A is a schematic diagram of a power module in accordance with yetanother embodiment.

FIG. 6B is a schematic diagram of a power module in accordance with afurther embodiment

FIG. 6C is a block diagram of a power module in accordance with anotherembodiment.

FIG. 7A is a schematic diagram of a power module in accordance with yetanother embodiment.

FIG. 7B is a block diagram of a power module in accordance with anotherembodiment.

FIG. 8A is a schematic diagram of a power module in accordance with yetanother embodiment.

FIG. 8B is a block diagram of a power module in accordance with anotherembodiment.

FIG. 9A is a cross-sectional view of a power module in accordance withan embodiment.

FIG. 9B is another view of a power module in accordance with anembodiment.

DETAILED DESCRIPTION

In various embodiments, a configurable power module may be provided thatbe used in different power conversion systems. There may be a generaldesign for the module such that it can be readily manufactured in highvolumes. Then, configurable aspects can be provided such that the powermodule can be implemented in particular power conversion systems.

While embodiments are not limited in this regard, power modulesmanufactured as described herein may be implemented in electric vehicle(EV) charging systems to realize direct connection to a grid network andgeneration of one or more sources of charging power that can be providedto one or more EV charging stations. In this way, EVs connected to an EVcharging station can be efficiently charged at a charging voltage and/orcharging current that may be dynamically controlled.

Referring now to FIG. 1A, shown is a block diagram illustrating anenvironment in which an EV charging system having power modules inaccordance with an embodiment may be used. More particularly in FIG. 1A,an EV charging system 100, which may be a distributed modular-basedcharging system, couples between a grid network 50 (represented bytransmission lines 52 and a distribution feeder 54) and multiple EVcharging stations 60 ₁-60 _(n) (also referred to herein as“dispensers”), each of which may be implemented with one or more EVdistributors to enable charging of an EV (representative EVs 65 ₁-65_(n) are shown in FIG. 1A).

More specifically, embodiments may be used for use with distributiongrid networks that provide power at medium voltage levels (e.g., betweenapproximately 1000 volts (V) and 35000V) and at a low frequency (e.g.,50 or 60 Hertz (Hz)). For ease of discussion, understand that the terms“grid,” “grid network” or “distribution grid network” are to be usedinterchangeably to refer to a power distribution system that providesmedium voltage power at low frequency. With embodiments herein, an EVcharging system such as charging system 100 may directly couple to amedium voltage distribution grid network (which may be an AC voltagegrid or a DC voltage grid) without an intervening power transformer.Stated another way, embodiments provide an EV charging system that canbe adapted to couple to a distribution grid network without a step uptransformer, also known as a power or distribution transformer.

In this way, EV charging system 100 may directly receive incoming gridpower with a grid voltage at a medium voltage level and a low frequency.As used herein, the terms “direct connection” and “direct coupling” withrespect to an EV charging system mean that this system receivesdistribution grid power at a distribution grid network-provided gridvoltage at a distribution grid network low frequency without presence ofintervening components. Note that an EV charging system may couple to agrid network through a line reactor, a fuse, a circuit breaker, and/or apower circuit disconnect, and still be considered to be in a “directcoupling” with the grid network.

With embodiments, a means is provided for charging electric vehicles orother moving objects. In implementations, high power fast charging maybe provided for electric vehicles by connecting to a medium voltage ACor DC distribution feeder. With an EV charging system as describedherein, use of components including large magnetics components such asdistribution transformer and in-line reactors may be avoided.

Still with reference to FIG. 1A, distribution feeder 54 of grid network50 may be a medium voltage AC or DC distribution feeder. As illustrated,distribution feeder 54 is directly coupled to EV charging system 100 viathree-phase connections.

Charging system 100 includes a grid-tie module 120. In embodimentsherein, grid-tie module 120 may be configured to receive grid power atan incoming grid voltage (which as described above may be an AC or DCvoltage) and perform an initial conversion of the incoming grid voltageto a voltage that is at different magnitude and/or frequency. Grid-tiemodule 120 may include one more configurable power modules as describedherein. Depending on implementation, grid-tie module 120 may convert theincoming grid voltage to one or more DC or AC voltages at differentmagnitude or frequency. To this end, grid-tie module 120 interfaces withmedium voltage AC or DC grid network 50 and utilizes power electronicsconverters to convert the AC or DC grid voltage to a voltage that is atdifferent magnitude and/or frequency. Grid-tie module 120 may includemultiple stages that may be isolated from each other. In otherimplementations, at least some of these stages may be cascaded togetherto increase voltage capabilities.

In particular embodiments herein, grid-tie module 120 may include powerelectronics-based converters to convert the incoming AC or DC gridvoltage. As an example, grid-tie module 120 may include so-calledH-bridge power converters to receive the incoming grid voltage andperform a voltage/frequency conversion, e.g., to a DC voltage. In turn,grid-tie module 120 may further include a first stage of a DC-DCconverter to convert the DC voltage to a high frequency AC voltage(e.g., a square wave voltage) at a given high frequency (e.g., between 5kilohertz (kHz) and 100 kHz).

As further illustrated in FIG. 1A, this high frequency AC voltage may beprovided to a transformer network 130. In the embodiment shown in FIG.1A, transformer network 130 includes multiple isolated transformers,each having a single primary winding and a single secondary winding. Inother implementations a transformer network may take the form of asingle transformer having a single primary winding and multiplesecondary windings. In either case, transformer network 130 isconfigured as a high frequency transformer, e.g., to operate atfrequencies between approximately 5 kHz and 100 kHz.

Still referring to FIG. 1A, the secondary windings of transformernetwork 130 each may be coupled to an electrically isolated vehiclecharger 140 ₁-140 _(n). In embodiments herein, each vehicle charger 140may be configured as a power electronics converter that converts thesecondary voltage output by transformer network 130 to a voltage (e.g.,DC) at a different frequency and/or magnitude. More particularly forvehicle charging as described herein, vehicle chargers 140 may includeDC-DC converters to provide charge capabilities to at least one EVcharging station 60.

Continuing with the above discussion in which an AC voltage is outputfrom transformer network 130, vehicle chargers 140 may include an AC-DCconverter as well as a DC-DC converter to provide charging capability ata desired charging voltage and/or charging current. Vehicle chargers 140may include one more configurable power modules as described herein.

As shown in FIG. 1A, EV charging system 100 may be coupled to chargingstations 60 via a plurality of output lines 55 _(1-n). Althoughdifferent connection topologies are possible (including directconnection as shown in FIG. 1B, discussed below), FIG. 1A shows animplementation in which each output line 55 is dedicated to a singlecharging station 60.

To effect control of EV charging system 100, at least one controller 150may be present. In various embodiments, controller 150 may include oneor more central processing units (CPUs) or systems on chip (SoCs), adedicated microcontroller or other programmable hardware control circuitsuch as programmable logic. In one embodiment, controller 150 may form adistributed control architecture. In any case, controller 150 may beconfigured to execute instructions stored in one or more non-transitorystorage media. Such instructions may cause controller 150 toautomatically and dynamically control charging voltages and/or chargingcurrents depending upon capabilities and requirements of chargingstations 60 and/or connected EVs 65.

Referring now to FIG. 1B, shown is a block diagram illustrating anotherenvironment in which an EV charging system having a configurable powermodule in accordance with an embodiment may be used. More particularlyin FIG. 1B, an EV charging system 100′ may be configured the same assystem 100 of FIG. 1A, with the sole difference being that system 100′provides vehicle charging connectors integrated therein such that outputlines 55 and charging stations 60 may be eliminated. Thus as shown inFIG. 1B, system 100′, via chargers 140 and integrated chargingconnectors, directly connect to EVs 65.

In still further implementations an EV charging system also may includecapabilities to provide load power to a variety of AC loads, such asindustrial facilities or so forth. In addition, the EV charging systemmay be configured to receive incoming energy, such as from one or morephotovoltaic arrays or other solar panels and provide such energy,either for storage within the EV charging system, distribution to thegrid and/or as charging power to connected EVs.

As described above, different configurations of EV charging systems arepossible. Referring now to FIG. 2 , shown is a block diagram of an EVcharging system in accordance with a particular embodiment. As shown inFIG. 2 , EV charging system 200 is a multi-port modular power converterthat uses a single transformer. In FIG. 2 , understand that a singlephase is illustrated for ease of discussion. In a given charging systemthere may be three phases, each configured as shown in FIG. 2 orcombined as a single transformer.

Incoming grid power is received at a given grid voltage via input nodes205 a, 205 b. Although embodiments are not limited in this regard, inFIG. 2 this grid voltage may be received as a medium AC voltage, e.g.,at a voltage of between approximately 1 and 50 kilovolts (kV) and at agrid frequency of 50 Hz or 60 Hz. As shown, an input inductance couplesto input node 205 a.

The incoming voltage is provided to a plurality of input stages, each ofwhich may include multiple H-bridge converters. More specifically, aplurality of input stages 210 ₁-210 _(n) are shown that are cascadedtogether. Each input stage may include a grid-side converter 212 _(1-n)(shown as an AC-DC converter). In turn each grid-side converter 212couples to a DC-AC converter 214 ₁-214 _(n) of a given DC-DC converter215 ₁-215 _(n). Thus each grid-side converter 212 receives an incominggrid AC voltage and converts it to a DC voltage, e.g., at the same ordifferent voltage magnitude. While embodiments may typically implementconverters 212 and 214 (and additional converters described below) thatare symmetric, it is also possible for there to be asymmetricconfigurations across power stages. Input stages 210 may include onemore configurable power modules as described herein.

In an embodiment, each grid-side converter 212 may be implemented as anH-bridge converter including low voltage or medium voltage switches,e.g., silicon carbide (SiC) devices. In other embodiments, eachgrid-side converter 212 may be formed as a multi-level rectifier. Theresulting DC voltages are in turn provided to corresponding DC-ACconverters 214 that act as an input stage of an isolated DC-DC converter215. In embodiments, converters 214 may be implemented as H-bridgeconverters to receive the DC voltage and convert it to a high frequencyAC voltage, e.g., operating at a frequency of up to 100 kHz. While asquare wave implementation is shown in FIG. 2 , understand that in othercases the AC voltage may be sinusoidal.

The high frequency voltage output from converters 214 may be provided toa corresponding primary winding of a transformer 220, namely a highfrequency transformer. While shown in FIG. 2 as a single transformerwith multiple primary windings and multiple secondary windings, in otherimplementations separate transformers may be provided, each with one ormore primary windings and one or more secondary windings.

In any event, the galvanically isolated outputs at the secondarywindings of transformer 220 may be provided to a plurality of outputstages 230 ₁-230 _(o). As such each output stage 230 includes an AC-DCconverter 232 ₁-232 _(o) (of a DC-DC converter 215). Thereafter, theoutput DC voltage may be further adjusted in magnitude in correspondingload-side converters 235 ₁-235 _(o) (and 235 ₁-235 _(o)). Output stages230 may include one more configurable power modules as described herein.

As illustrated, output stages 230 thus include a given output stage(namely stage 232) of a DC-DC converter 215 and a load-side converter235. As shown in FIG. 2 , multiple output stages 230 may couple togetherin cascaded fashion (e.g., either in a series connection as shown inFIG. 2 or in a parallel connection) to provide a higher output voltageand/or current depending upon load requirements. More specifically, afirst set of output stages 230 ₁-230 _(m) are cascaded together andcouple to output nodes 245 _(a,b). In turn, a second set of outputstages 230 ₁-230 _(o) are cascaded together and couple to output nodes245 _(1,o). The resulting outputs are thus at a given DC voltage leveland may be used as a charging voltage and/or current for connected EVs.While this particular arrangement with cascaded input and output stagesare shown in FIG. 2 , understand that a multi-port power converter maybe implemented in other manners such as using modular high frequencytransformers. Still further, understand that the actual included DC-DCconverters may have a variety of different topologies.

For example, in other cases a modular high frequency transformer may beused. Referring now to FIG. 3 , shown is a block diagram of an EVcharging system in accordance with another embodiment. As shown in FIG.3 , EV charging system 300 is a multi-port modular power converter thatuses a modular transformer. As in FIG. 2 , a single phase is illustratedfor ease of discussion.

Incoming grid power is received at a given grid voltage via input nodes305 a, 305 b. The incoming voltage is provided to a plurality of inputstages, each of which may include multiple H-bridge converters. Morespecifically, a plurality of power converter stages 310 ₁-310 _(n) areshown. Each stage 310 may include a grid-side converter 312 _(1-n)(shown as an AC-DC converter) and a DC-AC converter 314 ₁-314 _(n) of agiven DC-DC converter 315 ₁-315 _(n). Via independent transformers ofDC-DC converters 315, a resulting electrically isolated DC voltage isprovided to an AC-DC converter 332 ₁-332 _(n) and thereafter to aload-side converter 334 ₁-334 _(n). Note that operation may be similarto that discussed in FIG. 3 . In one embodiment, each load-sideconverter 334 ₁-334 _(n) may provide a voltage to the load, e.g.,connected electric vehicles. However here note that potentiallydifferent amounts of load-side converters 334 may be cascaded to providea given DC voltage to a load (e.g., EV charging station). As oneexample, a first set of load-side converters 334 ₁-334 _(j) may providea first charging voltage of approximately 1500 volts via output nodes345 a,b. And a second set of load-side converters 334 _(j+1)-334 _(n)may provide a second charging voltage of approximately 1000 volts viaoutput nodes 345 c,d. In an embodiment, the various converters mayinclude one more configurable power modules as described herein.

Referring now to FIG. 4A, shown is a schematic diagram of a power modulein accordance with an embodiment. More specifically in FIG. 4A, anintelligent power module 400 (generically referred to herein as a “powermodule”) is a configurable power module that can be implemented in awide variety of power conversion systems such as EV charging systems asdescribed above, among other systems such as solid state transformers,solar power converters, STATCOMs, etc.

In FIG. 4A, a particular configuration of power module 400 isillustrated, with certain connections to enable its adaptation into afirst type of power conversion system. More specifically in FIG. 4A,power module 400 is illustrated with connections to provide lowfrequency converters that are parallel connected and high frequencyconverters that have independent output connections.

The configuration shown in FIG. 4A provides for parallel-connected lowfrequency H-bridges that may have typical operation parameters of 800Volts AC (VAC), line-to-line, rated 0-375 Amperes (A), and whenconfigured for DC operation may operate at 800 VDC and 0-375 A. Withrespect to the high frequency bridges, they may be arranged in the FIG.4A embodiment as independent high frequency H-bridges that may operateat typical levels of 0-800 VAC and at 125A each. Further, these highfrequency bridges may operate at higher frequencies, e.g., atapproximately 40 kilohertz (kHz).

As will be described further herein, in the configuration of FIG. 4Athere are jumpers or other interconnection members that couple variouscomponents within power module 400, which may distinguish thisimplementation from other configurations described below. A controller(not shown for ease of illustration in FIG. 4A) may control power module400 for parallel operation, after a base power module is adapted andconfigured as shown in FIG. 4A, which may occur in a factory setting.

Regarding the configuration of power module 400, incoming power isreceived via input lines 440A,B from an input power source, such as autility grid that operates at, e.g., 50 or 60 Hertz (Hz). To providethis voltage in parallel to the multiple bridges or stages, lines 440A,Bcouple to common input nodes 445 _(1,2), which as seen couple to inputconnection points 430 ₁₋₃. This input power is in turn provided to aplurality of input or first stages 410 ₁₋₃ (note that as used herein,the terms “bridge,” “H-bridge” and “stage” are used interchangeably torefer to switching circuitry that performs a power conversion operation;however understand that in the above examples of EV charging systems,the term “stage” also may refer to collections of converters such as theAC-DC and DC-DC converters shown in FIGS. 2 and 3 ).

As seen, the plurality of first stages 410 ₁₋₃ are implemented as lowfrequency H-bridges that receive the incoming power and are connected inparallel. In turn, each first stage 410 couples to a corresponding DCbus 415 ₁₋₃. DC buses 415 may be implemented as capacitors that in anembodiment may be on the order of between approximately 600V and 1200V.These DC buses are each in turn coupled to a corresponding one of aplurality of output or second stages 420 ₁₋₃. In embodiments, eachsecond stage 420 may be implemented as an H-bridge that is independentlyconnected and thus provides output of an AC voltage at a plurality ofoutput connections 460 ₁₋₃.

To enable the parallel interconnection shown in FIG. 4A while providinga single power module that may be used in a variety of differentconfigurations (including series-connected low frequency stages and soforth), certain interconnections may remain unconnected in FIG. 4A. Morespecifically as shown in FIG. 4A, a plurality of so-called jumperconnection points 431 ₁₋₃ and 436 ₁₋₃ (among others) are unconnected inthis arrangement. However, in other configurations of the sameconfigurable power module, these points may be interconnected in a givenmanner using interconnection members such as jumpers or other conductivemembers, zero ohm resistors or so forth. Note that additionalinterconnection members also may be present in this and otherimplementations.

Thus with embodiments, the configurability of power module 400 may berealized, at least in part, by different connection points that can beconnected or unconnected depending on desired configuration. In theillustration of FIG. 4A, on a front end side, these connection pointsinclude input connection points 430 and jumper connection points 431 and436; of course additional such connection points may be present. In anembodiment, each of these connection points can be implemented on acircuit board as a physical connector, contact or other conductivemember to which a cable, wire or another conductive member such as ajumper wire connector or zero ohm resistor may couple.

As further shown with regard to these connection points, certainreference indicators are shown in FIG. 4A, such as LF-1A associated withinput connection point 430 ₁ and HF-1A associated with output connection460 ₁. These indicators identify interconnectivity nodes for a first lowfrequency converter (i.e., LF-1A) and a first high frequency converter(i.e., HF-1A). These reference indicators may be used to map theconfiguration in FIG. 4A to a block level view of the configurationshown in FIG. 4B, discussed below.

To enable the incoming parallel-connected power to be provided to firststages 410, a jumper is provided on each input path from inputconnection point 430 to first stage. Specifically as shown in FIG. 4A, ajumper is provided that couple between connection points LF-E and LF-D(generically). Note that in other implementations, a parallelconfiguration for a power module can be realized without using anyjumpers. Stated another way, a single power module design can providevarious interconnection points, where depending on desiredconfiguration, none, some or possibly all interconnection points may beelectrically connected via jumpers or other interconnection members, toeffect the desired configuration.

With embodiments, a single intelligent power module design may bemanufactured. Then based on factory configuration for a particular powerconversion system in which the power module is to be adapted, a varietyof different power module configurations can be realized. In addition toproviding a single power module that can be used in different systems,understand that the intelligent power module also may be dynamicallycontrolled to operate with unidirectional and bidirectional power flows.

Furthermore, this single power module may be used to implement bothAC-DC conversion and DC-DC and DC-AC and AC-AC conversion, without anychange in the actual components of the power module. Also, first stages410 and second stages 420 may be implemented using commerciallyavailable transistors. Although embodiments are not limited in theregard, in one implementation these transistors may be insulated gatebipolar transistors (IGBTs). In one embodiment, these commerciallyavailable IGBTs may be formed in a package having the transistor and adiode in parallel. In other implementations, the transistors may besilicon metal oxide semiconductor field effect transistors (MOSFETs),silicon carbide (SiC) MOSFETs or Gallium Nitride (GaN) MOSFETs, as otherexamples. This use of commercially available devices stands in contrastto many types of available power modules in which custom designs areneeded to configure the power module for a particular systemimplementation. As such, ease of design and incorporation into differentsystems may be realized. Also in this way reduced component counts,bills of material and reduced time to market can be realized.

Further, to enable the ability to effectively bypass certain circuitswithin power module 400, e.g., in case of a failure, various sensing andadditional switching capabilities are provided. Specifically as shown inFIG. 4A, a plurality of current sensors 438 ₁₋₃ and 450 ₁₋₃ may becoupled to inputs of first stages 410 and outputs of second stages 420.In addition, switching circuitry 437 ₁₋₃ and 452 ₁₋₃ connected to firststages 410 and second stages 420 may be used to selectively isolatevarious circuitry of power module 400, e.g., due to a detectedmalfunction or other failure. Such operation may occur under control ofa controller (not shown for ease of illustration in FIG. 4A). By way offeedback information provided by sensors 438, 450 and gate driversmonitoring signals (not shown), this controller may detect such failureand control power module 400 accordingly, as will be described furtherbelow.

Still with reference to FIG. 4A, the configurable nature of power module400 further may be realized, in an embodiment, by way of incorporationof virtually all of the above-described circuitry on a single printedcircuit board that by itself may in some cases form an enclosure forpower module 400. With regard to FIG. 4A, input lines 440A,B and outputlines 460 ₁₋₃ may be the only components that are not implemented on thesingle circuit board. Of course other implementations are possible;however, by way of this arrangement a single configurable power modulemay be realized that can be incorporated into a wide variety ofdifferent systems.

Referring now to FIG. 4B, shown is a block diagram of a power module inaccordance with an embodiment. In the illustration of FIG. 4B, the samepower module 400 is illustrated in block diagram form. Thus a pluralityof first stages 410 ₁₋₃ are illustrated that are implemented asparallel-connected low frequency bridges that couple via DC buses (notshown for ease of illustration in FIG. 4B) to a plurality of secondstages 420 ₁₋₃ that are implemented as high frequency bridges.

FIG. 4B further illustrates a control circuit 470 that may be used toprovide configuration and switching control to various components ofpower module 400 to enable proper interconnection and operation for agiven use case. Control circuit 470 may be a hardware circuit such asone or more general-purpose processors and/or field programmable gatearrays (FPGAs) or other programmable circuitry to execute instructionsthat are stored in a non-transitory storage medium (also present in thepower module). Responsive to the instructions (and possibly feedbackinformation), control circuit 470 may perform various configuration andcontrol operations for power module 400.

Still with reference to FIG. 4B, in this arrangement, the various inputand output connections into and out of first stages 410 may be realizedwith a single jumper (coupled between nodes LF-D and LF-E, such as LF-1Dand LF-1E). In turn, there are no jumpers present in second stages 420.Note that the various identified nodes (such as LF-1A, HF-1A) and soforth refer to the same nodes identified in the schematic diagram ofFIG. 4A that may be implemented as various connection points. Thus forsake of exemplary illustration, inputs (Parallel 1A-3A and Parallel1B-3B) map to input connection points 440A,B, respectively, of FIG. 4A,and similarly outputs (HF1A,1B-HF3A,3B) map to output connections 460₁₋₃, respectively, of FIG. 4A.

In another configuration, the same power module, by way of differentinterconnection of the same circuitry (such as by way of differentjumpers or other interconnect members) may be configured forseries-connected low frequency bridges that may operate as an ACconverter or DC converter.

Referring now to FIG. 5A, shown is a schematic diagram of a power modulein accordance with another embodiment. Power module 500 of FIG. 5Aincludes the same components as power module 400 of FIG. 4A, but withdifferent interconnections to provide a power module havingseries-connected low frequency converters. Given the similarity, thecommon components are not further discussed, and understand thatreference numerals used in FIG. 5A generally refer to the samecomponents as in FIG. 4A, albeit of the “500” series in place of the“400” series of FIG. 4A.

In this configuration, the AC/DC series-connected arrangement of firststages 510 may be realized by providing jumpers or other interconnectsat the inputs of the stages. Thus as shown in FIG. 5A, a first seriesjumper is coupled between nodes LF-1B and LF-2A to series connect firststage 510 ₁ to second stage 510 ₂. And in turn, a second series jumperis coupled between nodes LF-2B and LF-3A to series connect second stage510 ₂ to third stage 510 ₃. Additional jumpers are also connectedinternally to each stage, such as the jumper coupled between connectionnodes LF-1C and LF-1E.

With the arrangement of FIG. 5A, the series-connected low frequencyH-bridges may have typical operation parameters of 2400 VAC,line-to-line, rated 125 A, and when configured for DC operation mayoperate at up to 2400 VDC, and 125 A. The high frequency bridges mayoperate the same as in the FIG. 4A embodiment, namely as independenthigh frequency H-bridges that may operate at typical levels of 0-800 VACand at 125 A each.

As further illustrated, bypass operation is possible in thisimplementation. Specifically here, bypass jumpers couple between nodes530 and 535, such that when enabled, a given first stage 510 may bebypassed. Such bypass operation may occur in response to detection of afault, which may trigger closing of a switch (e.g., relay) 537 to effectthe bypass via connected jumpers.

Referring now to FIG. 5B, shown is a block diagram of a power module inaccordance with an embodiment. In the illustration of FIG. 5B, powermodule 500 is shown with the different jumper connections to provideboth a series configuration of low frequency stages and bypasscapabilities. Note that in FIG. 5B, the identified nodes to which thesejumpers connect are shown in the schematic diagram of FIG. 5A.

And still further configurations are possible. For example, DC or ACsingle or three phase/independent DC buck/boost circuits may be realizedusing yet another configuration of an intelligent power module inaccordance with an embodiment. In such arrangements, the low frequencystages may be AC or DC series-connected by way of jumpers to enableoperation at 800 V, 375 A.

Referring now to FIG. 6A, shown is a schematic diagram of a power modulein accordance with yet another embodiment. Power module 600 of FIG. 6Aincludes the same components as power module 400 of FIG. 4A, but withdifferent interconnections to provide a power module having controllablebuck/boost/EV low frequency converters. Given the similarity, the commoncomponents are not further discussed, and understand that referencenumerals used in FIG. 6A generally refer to the same components as inFIG. 4A, albeit of the “600” series in place of the “400” series of FIG.4A.

In this configuration, first stages 610 are coupled in a buck/boostconfiguration via buck/boost jumpers which, as shown, enable coupling ofthe different sides of the H-bridges. In this arrangement, parallel topIGBTs and bottom IGBTs are controlled for a buck/boost converter. Notethat these first stages can be coupled to receive a grid voltage (e.g.,an AC or DC grid voltage). Or in this buck/boost arrangement, firststages 610 may be controlled to provide a DC voltage, to be provided toa battery in an EV implementation.

Also note in the embodiment of FIG. 6A, first stages 610 areindependently connected. In different implementations by control ofjumpers, first stages 610 can be connected in parallel or serial, andmay be coupled to an AC or DC grid, as described above. By appropriatecontrol of IGBTs, this single system can be used in both DC and ACapplications.

For an AC application, the operation is the same as the series andparallel configurations described above with respect to power modules400 and 500. For connection to a MV DC grid (in the grid-side section)and for an EV application, jumper settings for a buck/boost/EV mode areapplicable, such that the switches are controlled to allow forbidirectional buck/boost converter operation.

As further shown, connection to external reactance (an off-boardinductor Re1-3) may be provided by way of a pair of jumpers (coupling toconnection nodes LF-D and LF-E, generically). Another jumper betweenLF-E and LF-F (generically) may be used to couple a filter capacitor.Further, connection to a given system (e.g., an EV charger) via DCvoltage nodes 680 ₁₋₃ may be effected by coupling to additionalconnection nodes (e.g., LF-1A and LF-DC-1 in the top stage 610 ₁) Asfurther shown in this configuration, an additional jumper (jumper E12 inthe top stage 610 ₁) couples between connection points LF-C and LF-B(generically).

In the alternate embodiment of FIG. 6B, a power module 600′ may beconfigured the same with respect to the low frequency stages as powermodule 600. However in this embodiment, note that high frequency stages630 have a common neutral point connection for 3-phase AC operation.

Thus it is further possible to configure high frequency stages 630 tohave a buck/boost configuration by similarly providing buck/boostjumpers between the different sides of the H-bridges of these stages.With this arrangement, power module 600 can be implemented as an EVcharger to provide a charging voltage and/or current to one or more EVs.

Referring now to FIG. 6C, shown is a block diagram of a power module inaccordance with an embodiment. In the illustration of FIG. 6C powermodule 600 is illustrated with the different jumper connections toprovide a buck/boost configuration of low frequency stages. Note that inFIG. 6C, the identified nodes to which these jumpers connect are shownin the schematic diagram of FIG. 6A.

In yet another implementation, a three phase AC converter may berealized by way of appropriate use of jumpers. In this way, anintelligent power module may operate at 480 VAC with three phaseinput/output connections and at a current capacity of 125 A. Note thatthree level input/output arrangement is optional.

Referring now to FIG. 7A, shown is a schematic diagram of a power modulein accordance with yet another embodiment. Power module 700 of FIG. 7Aincludes the same components as power module 400 of FIG. 4A, but withdifferent interconnections to provide a power module that can be used asa three phase AC converter. Given the similarity, the common componentsare not further discussed, and understand that reference numerals usedin FIG. 7A generally refer to the same components as in FIG. 4A, albeitof the “700” series in place of the “400” series of FIG. 4A.

To effect this three phase arrangement, note that different AC inputsconnect to input connection points 730 ₁₋₃, and a common neutral couplesto connection points 735 ₁₋₃ of first stages 710. It is also possible toprovide optional DC bus jumpers to the connection points illustrated inFIG. 7A. Similar coupling of a common neutral occurs at outputs ofsecond stages 720.

Referring now to FIG. 7B, shown is a block diagram of a power module inaccordance with an embodiment. In the illustration of FIG. 7B, powermodule 700 is illustrated with the different jumper connections toprovide neutral point connection in a three phase AC converterconfiguration. Note that in FIG. 7B, the identified nodes to which thesejumpers connect are shown in the schematic diagram of FIG. 7A.

In still further embodiments, a multi-function power module may berealized by providing individually controlled and electrically isolateddual active bridge input/output connections. In this way selectable24-800 VDC or 120 VAC to 480 VAC input/output connections may berealized with switching speeds of up to 80 kHz per stage.

Referring now to FIG. 8A, shown is a schematic diagram of a power modulein accordance with yet another embodiment. Power module 800 of FIG. 8Aincludes the same components as power module 400 of FIG. 4A, but withdifferent interconnections to provide a power module that can be used asa multi-function converter. Given the similarity, the common componentsare not further discussed, and understand that reference numerals usedin FIG. 8A generally refer to the same components as in FIG. 4A, albeitof the “800” series in place of the “400” series of FIG. 4A. In FIG. 8A,dual inputs may be provided by way of input connection points 830 ₁₋₃and 836 ₁₋₃. In other aspects, the configuration may be as in FIG. 4A.

Referring now to FIG. 8B, shown is a block diagram of a power module inaccordance with an embodiment. In the illustration of FIG. 8B, powermodule 800 is illustrated to show the input/output connections for thismulti-function module.

Referring now to FIG. 9A, shown is a cross-sectional view of a packagingarrangement of a configurable power module in accordance with anembodiment. As shown in FIG. 9 , configurable power module 900 isimplemented as a folded power module in which a circuit board on whichthe power module is adapted itself forms the enclosure. In FIG. 9A, across-sectional view is shown in which a circuit board is folded suchthat a first portion 910 and a second portion 930 are adapted tomaintain power conversion stages, while another portion 920 is adaptedto maintain control circuitry among other such circuitry.

In the high level view in FIG. 9A, the circuit board is folded via flexportions 915 such that portion 920 forms a central portion and portions910 and 930 are peripheral portions. Note that in the implementationshown, the circuit board in turn may be formed into a fully enclosedpower module via frame members 970. However this enclosure arrangementmay be optional in some cases.

By way of folding the circuit board, the circuit board may provideprotection to components of the power module, as the components areadapted in the interior of the formed construction. More specifically,the various switches of the power stages may be adapted on the circuitboard portions and in turn, heat sinks may be adapted over the switches.In the embodiment shown, each independent heat sink 940 may beassociated with a given switch 945 (e.g., IGBT) of a stage. That is, inan embodiment an independent heat sink may be present for each IGBT orother switch of the first stages and second stages. Thus with referenceback to, e.g., FIG. 8A, there may be 24 individual heat sinks, eachassociated with one of the IGBTs.

Still with reference to FIG. 9A, additional components, including DC buscomponents (e.g., capacitors 960) and gate drivers 950 may be adapted onthe different portions. Also understand while not shown in the highlevel view of FIG. 9A, various sensors, switches, connection points andso forth also may be adapted on the circuit board.

Referring now to FIG. 9B, shown is another view of a power module inaccordance with an embodiment. As shown in FIG. 9B, power module 900 isshown in an unfolded arrangement in which a circuit board includes afirst peripheral portion 910, central portion 920, and second peripheralportion 930. As further detailed in this view, a plurality of heat sinks940 are present and associated with the various switches.

Note that with independent heat sinks for each transistor,cross-coupling may be reduced or eliminated. These heat sinks may benon-conductive, e.g., formed of aluminum. Furthermore, the heat sinksgiven their base design, off-the-shelf heat sink components may be used.In some cases, additional cooling may be realized by providing a fluidcooling mechanism in which various fluid pipes or so forth may beadapted throughout the unit. These conduits may then be coupled via acommon coupling point such as a manifold, from which connection may bemade to an external heat exchanger, as one example.

In an embodiment, the circuit board may be manufactured as a flex cardwith rigid portions and flexible portions. In the view of FIG. 9B allportions 910, 920 and 930 may be formed as rigid portions, and flexportions 915 formed of a flex material adapted therebetween, to enablethe folding as described above. As an example, flex portions 915 may beimplemented using a polyamide film without any rigid material adaptedthereon, to enable its flexing and to realize the folded configurationherein. As one example, a circuit board may be implemented as amulti-layer circuit board to provide internal interconnection betweenvarious points on which components are adapted.

Note by way of a folded configuration as described herein, cooling maybe enhanced due to improved airflow. Further benefits of a foldedconfiguration as herein described may include reduced noise andincreased power density.

Understand while not shown for ease of illustration in FIGS. 9A and 9B,additional components, such as fiber optic communication units, jumpersand so forth may be adapted on the exterior of power module 900, furtherenhancing airflow within the internal portion.

There may be additional advantages to a folded power module as describedherein. As examples, easy adaptation of various circuit arrangementsincluding series and parallel can be realized. This is so, for example,since with a series connection, a neutral point can be easily accessedby multiple converters. Further, a grounded neutral point of a centercan balance common mode voltage of the upper and lower stages.Furthermore, for redundancy purposes, a redundant DC/DC converteroperating at low voltage, e.g., 5V, may be run off of a given DC powerbus. Therefore, if a given power supply should fail, the unit may stilloperate. And as described above, there are various features to enable abypass or bridge around a failure.

While the present disclosure has been described with respect to alimited number of implementations, those skilled in the art, having thebenefit of this disclosure, will appreciate numerous modifications andvariations therefrom. It is intended that the appended claims cover allsuch modifications and variations.

1. A power module for use in an electric vehicle (EV) charging system,the power module comprising: a circuit board having adapted thereon: aplurality of first stages, each of the plurality of first stages coupledto one of a first plurality of connector points to couple a firstvoltage at a first frequency and comprising an H-bridge to convert thefirst voltage to a DC voltage; a plurality of DC buses, each of theplurality of DC buses coupled to receive the DC voltage from one of theplurality of first stages; a plurality of second stages, each of theplurality of second stages coupled to one of the plurality of DC busesto receive the DC voltage and output a second voltage at a secondfrequency; and a hardware configuration system having fixed componentscomprising a plurality of jumper connector points, each of a first setof the plurality of jumper connector points to couple to one of thefirst plurality of connector points and each of a second set of theplurality of jumper connector points to couple to one of the pluralityof first stages, wherein the power module is a configurable module, and:when the configurable module is adapted in a first EV charging system,the hardware configuration system includes the fixed components andoptional components comprising one or more jumpers coupled to at leastsome of the plurality of jumper connector points; and when theconfigurable module is adapted in a second EV charging system, thehardware configuration system includes the fixed components and not theoptional components.
 2. The power module of claim 1, wherein when theconfigurable module is adapted in the second EV charging system theplurality of jumper connector points are unconnected.
 3. The powermodule of claim 2, wherein when the configurable module is adapted inthe first EV charging system, the plurality of first stages are coupledin series via the one or more jumpers coupled to the first set of theplurality of jumper connection points.
 4. The power module of claim 1,wherein the one or more jumpers comprise a first set of jumpers toserialize the plurality of first stages.
 5. The power module of claim 4,wherein the one or more jumpers further comprise a second set of jumperscoupled to the plurality of first stages to enable a bypass operation tooccur.
 6. The power module of claim 1, further comprising a controllercoupled to the plurality of first stages and the plurality of secondstages, wherein the controller, in a first mode, is to configure thepower module for unidirectional power flow to provide at least one of acharging current or a charging voltage to at least one EV coupled to theEV charging system, and, in a second mode, is to configure the powermodule for bidirectional power flow to provide the at least one of thecharging current or the charging voltage to the at least one EV or toprovide power from the at least one EV to a distribution grid network.7-10. (canceled)
 11. The power module of claim 1, wherein: when theconfigurable module is adapted in the first EV charging system, theconfigurable module is configured as an AC-AC converter; and when theconfigurable module is adapted in the second EV charging system, theconfigurable module is configured as an DC-AC converter. 12-20.(canceled)
 21. The power module of claim 6, further comprising aplurality of current sensors adapted to the circuit board, wherein basedat least in part on sensing information from one or more of theplurality of current sensors, the controller is to cause at least one ofthe plurality of first stages to be bypassed.
 22. The power module ofclaim 1, wherein the circuit board forms an enclosure for the powermodule.
 23. The power module of claim 1, wherein when the configurablemodule is adapted in the first EV charging system: the plurality offirst stages are coupled in parallel to receive AC power at a gridfrequency directly from a distribution grid network without anintervening low frequency transformer; and the plurality of secondstages are independently coupled to at least one high frequencytransformer, wherein each of the plurality of second stages is toprovide the AC power at a high frequency to the at least one highfrequency transformer.
 24. The power module of claim 1, furthercomprising a second configurable module, wherein when the secondconfigurable module is adapted in the first EV charging system, aplurality of first stages of the second configurable module are toprovide a DC charging voltage to at least one EV coupled to the first EVcharging system.
 25. The power module of claim 1, further comprising asecond configurable module, wherein when the second configurable moduleis adapted in the second EV charging system, a plurality of secondstages of the second configurable module are to provide at least one ofa charging voltage or a charging current to at least one EV coupled tothe second EV charging system.
 26. The power module of claim 1, furthercomprising: a plurality of first switches, each of the plurality offirst switches to selectively cause a corresponding one of the pluralityof first stages to be bypassed; and a plurality of second switches, eachof the plurality of second switches to selectively cause a correspondingone of the plurality of second stages to be bypassed.
 27. The powermodule of claim 1, wherein: when the configurable module is adapted inthe first EV charging system, the configurable module is configured asan AC-AC converter; and when the configurable module is adapted in thesecond EV charging system, the configurable module is configured as anAC-DC converter.
 28. An electric vehicle (EV) charging systemcomprising: a first circuit board having a plurality of layerscomprising conductive traces, the first circuit board having adaptedthereon: a plurality of low frequency (LF) bridge circuits, each of theplurality of LF bridge circuits to receive an incoming voltage directlyfrom a distribution grid network and output a DC voltage; a plurality ofDC buses, each of the plurality of DC buses coupled to receive the DCvoltage from one of the plurality of LF bridge circuits; a plurality ofhigh frequency (HF) bridge circuits, each of the plurality of HF bridgecircuits coupled to one of the plurality of DC buses to receive the DCvoltage and output a second voltage at a high frequency to at least onehigh frequency transformer; and a hardware configuration systemcomprising a plurality of jumper connector points, wherein: when theplurality of LF bridge circuits are to couple in parallel for a firstconfiguration, each of the plurality of LF bridge circuits comprises afirst jumper coupled between a first jumper connector point and a secondjumper connector point to provide the incoming voltage to a midpoint ofa first side of the corresponding LF bridge circuit; and when theplurality of LF bridge circuits are to couple in series for a secondconfiguration, each of the plurality of LF bridge circuits comprises asecond jumper coupled between the first jumper connector point and athird jumper connector point, and the second jumper connector point isunconnected; and a second circuit board having the plurality of layerscomprising the conductive traces, the second circuit board havingadapted thereon: a second plurality of HF bridge circuits, each of thesecond plurality of HF bridge circuits coupled to the at least one highfrequency transformer to receive a high frequency AC voltage from the atleast one high frequency transformer and output a second DC voltage; asecond plurality of DC buses, each of the second plurality of DC busescoupled to receive the second DC voltage from one of the secondplurality of HF bridge circuits; and a second plurality of LF bridgecircuits, each of the second plurality of LF bridge circuits to receivethe second DC voltage and output at least one of a charging voltage or acharging current to at least one EV dispenser to enable one or more EVsto be charged.
 29. The EV charging system of claim 28, wherein the firstcircuit board and the second circuit board have a common design.
 30. Thepower module of claim 1, wherein the H-bridge of the plurality of firststages is configured as a buck boost converter via a jumper coupled to afirst one of the second set of the plurality of jumper connector pointsand a second one of the second set of the plurality of jumper connectorpoints, to couple a midpoint of a first side of the H-bridge to amidpoint of a second side of the H-bridge.
 31. The power module of claim30, further comprising at least one other jumper to couple the midpointof the first side of the H-bridge to an external inductor.
 32. The powermodule of claim 1, wherein when the configurable module is adapted inthe first EV charging system, the one or more jumpers comprises a firstjumper to couple a midpoint of a first side of the H-bridge of a firststage of the plurality of first stages to a negative side of the DC busof the first stage.
 33. The power module of claim 32, wherein when theconfigurable module is adapted in the first EV charging system, the oneor more jumpers further comprises a second jumper to couple the midpointof the first side of the H-bridge to a midpoint of a second side of theH-bridge.
 34. The power module of claim 33, wherein when theconfigurable module is adapted in the first EV charging system, the oneor more jumpers further comprises a third jumper to couple the midpointof the second side of the H-bridge to a midpoint of a first side of anH-bridge of a second stage of the plurality of first stages.
 35. Thepower module of claim 32, wherein in the first EV charging system, theplurality of first stages are coupled in series.